PRIN. OF INTERNAL COMBUSTION ENGINES - OD1619 LESSON 1/TASK 1
level. They have excellent crosscountry performance capabilities over all types
of terrain where tactical or combat operations can be conducted. This includes
snow and ice, rocky terrain, swamps, and desert sands. In order to negotiate water
barriers with a minimum of preparation, all sensitive equipment is either
permanently waterproofed or designed to function underwater.
The majority of the vehicles described in the paragraphs above have an internal
combustion engine. For this reason, a mechanic should know the principles of
operation of this engine and its various components. An internal combustion engine
is any engine within which the fuel is burned. The four stroke and two stroke
cycle gasoline and diesel engines are examples of internal combustion engines
because the combustion chamber is located within the engine. In this task, an
internal combustion engine, referred to as the piston engine, will be described.
2.
Piston Engine Characteristics
a.
(1) General. Because the most widely used piston engine is the four stroke cycle
type, it will be used as the example for this paragraph and as the basis for
comparison in Task 2. The operation of the piston engine can best be understood by
comparing it to a simple cannon. In view A of figure 1 on the following page, a
cannon barrel, charge of gunpowder, and a cannonball are illustrated. In view B of
figure 1, the gunpowder is ignited. The gunpowder burns very rapidly and as it
burns there is a rapid expansion of the resulting gases. This rapid expansion
causes a tremendous increase in pressure that forces the cannonball from the barrel.
In view A of figure 2 on the following page, the cannon barrel has been replaced by
a cylinder and a combustion chamber. The cannonball has been replaced by a piston.
A mixture of vaporized fuel and air has replaced the gunpowder. In view B of
figure 2, the gasoline is ignited. This time, the resulting force acts to push the
piston downward.
2
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